In a wireless communication node, such as a TDD repeater designed to operate with a TDD based wireless system capable of simultaneous transmission and reception of TDD packets, the orientation of the antenna units is crucial in establishing non-interfering operation as it is critical that the receiver is not desensitized by the transmitted signals. Further, enclosing antenna modules and repeater circuitry within the same package is desirable for convenience, manufacturing cost reduction and the like, but such packaging can give rise to interference problems.
In a full duplex repeater package for use in a TDD system, one antenna or set of antennae may operate with, for example, a base station, and another antenna operates with a subscriber. Since the frequency for the TDD repeater may be the same, or at least may be very close in frequency for both sides of the repeater, isolation becomes important particularly when simultaneous transmission and reception on both sides of the repeater are performed. Further, since the repeater unit houses all circuitry within a single package, it is desirable to closely position the antennae with minimal antenna-to-antenna interaction while maintaining acceptable gain and in many cases acceptable directivity. Directivity in antennae is desirable for use in links where the direction of the signal arrival will not vary, or at least will vary infrequently such as in a link from a repeater to a base station or Access Point (AP). Difficulties arise however, in that the use of antennae with high directivity requires that directional alignment with the base station or AP be performed, typically by trial-and-error manual alignment.
For ease of manufacture, an exemplary repeater should be configured such that it can be easily produced in high volume manufacturing operations using low cost packaging. The exemplary repeater should be simple to set up to facilitate easy customer operation. Additional problems arise however when packaging repeater antennae and circuitry in close proximity. First, it becomes difficult to achieve high isolation between antennae due solely to the close physical proximity even where directional antennae are used. Isolation becomes even more difficult where antennas having omni directional antenna patterns are used and where the proximity of the repeater to structures such as walls, furniture or other objects cannot be anticipated, and thus cannot be compensated for in advance due to unknown such as the final placement of the repeater module.
Simply put, as the antennae are placed closer together, the more likely the antennae will couple energy into each other, which reduces the isolation between the sides of the repeater. Maintaining an omni or semi-omni directional antenna pattern becomes difficult since overlapping radiation patterns of antennae which are placed close to each other tend to generate interference effects. Energy from the antennae can further be electrically coupled through circuit elements such as through a shared ground plane especially in configurations where multiple antennas are integrated and the ground plane is small. While the use of direction antenna can benefit the repeater in terms of increased range and reduced wireless signal variation due to Raleigh fading effects, directional antennas are not typically used for indoor applications, due to the requirement for directional alignment, which is beyond the capability or desire of the average user.
Some improvements can be obtained through cancellation or similar techniques where a version of a signal transmitted on one side of the repeater is used to remove the same signal if it appears on the other side of the repeater. Such cancellation however can be expensive in that additional circuitry is required, and can be computationally expensive in that such cancellation can result in the introduction of a delay factor in the repeater or alternatively can require the use of more expensive and faster processors to perform the cancellation function.